Assessing Risks to Sea Otters and the Exxon Valdez Oil Spill: New Scenarios, Attributable Risk, and Recovery
Authored by Mark A Harwell, John H Gentile
Date Published: 2014
DOI: 10.1080/10807039.2013.828513
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Abstract
The Exxon Valdez oil spill occurred more than two decades ago, and the
Prince William Sound ecosystem has essentially recovered. Nevertheless, discussion continues on whether or not localized effects persist on sea
otters (Enhydra lutris) at northern Knight Island (NKI) and, if so, what
are the associated attributable risks. A recent study estimated new
rates of sea otter encounters with subsurface oil residues (SSOR) from
the oil spill. We previously demonstrated that a potential pathway
existed for exposures to polycyclic aromatic hydrocarbons (PAHs) and
conducted a quantitative ecological risk assessment using an
individual-based model that simulated this and other plausible exposure
pathways. Here we quantitatively update the potential for this exposure
pathway to constitute an ongoing risk to sea otters using the new
estimates of SSOR encounters. Our conservative model predicted that the
assimilated doses of PAHs to the 1-in-1000th most-exposed sea otters
would remain 1-2 orders of magnitude below the chronic effects
thresholds. We re-examine the baseline estimates, post-spill surveys, recovery status, and attributable risks for this subpopulation. We
conclude that the new estimated frequencies of encountering SSOR do not
constitute a plausible risk for sea otters at NKI and these sea otters
have fully recovered from the oil spill.
Tags
ecosystems
California
Causal inference
Prince-william-sound
Pacific regime shifts
North pacific
Population
declines
Gravel beaches
Killer whales
Alaska